Method and apparatus for determining a network search parameter in a mobile communications network

ABSTRACT

The present disclosure provides a method for more efficiently managing a mobile communications network by varying the frequency with which a mobile terminal searches for a home network.

RELATED APPLICATIONS

The present application is a National Phase entry of PCT Application No.PCT/GB2015/050312, filed on Feb. 5, 2015, which claims priority to EPPatent Application No. 14250018.0, filed on Feb. 6, 2014, which arehereby fully incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method of operating a mobilecommunications network, and in particular to a method of operating amobile communications network which comprises a plurality of microcellsalongside other mobile communications networks which comprise aplurality of macrocells.

BACKGROUND

FIG. 1 shows a schematic depiction of a mobile communications network100 which comprises a first plurality of microcells 110 and a secondplurality of macrocells 120. One macrocell will cover a substantiallylarger area than a microcell and thus it will be appreciated that thenetwork 100 may comprise many more microcells than macrocells. Operatorsof conventional mobile communications networks deploy microcells inareas where there are high levels of network use, for example in citycenters, shopping malls, transport interchanges. However, there is thepossibility that a first organization is operating the plurality ofmicrocells and that a second organization is operating the plurality ofmacrocells. In such a scenario, customers of the first organizationwould have their calls and data sessions routed via a microcell whenthey are within the coverage of a microcell. When the customers wereoutside of the range of a microcell then their calls and data sessionswould be routed via a macrocell, with a roaming agreement being in placebetween the first and second organizations. Thus, it can be seen thatthe first organization will be motivated for its customers to connectvia a microcell in preference to via a macrocell whenever possible.

Firstly, it is likely that users connected via a microcell willexperience a better throughput of data (as typically there will be fewerusers in a microcell than in a macrocell and thus the bandwidthavailable within a microcell is likely to be greater than that within amacrocell on a per user basis). Furthermore, there is a commercialdriver for the first organization as it will be cheaper to route datavia the microcells as it will not have to pay roaming charges to thesecond organization for routing data via the macrocells.

US 2012/0015651 discloses a method of determining a network searchfrequency in the situation where a user terminal moves from a locationwhere there is network coverage to a second location which is outside ofthe service area provided by the network. US 2011/0124334 discloses amethod of cell re-selection when moving from one location to a secondlocation within a defined network.

SUMMARY

According to a first aspect of the present disclosure there is provideda method of operating a mobile communications network, the methodcomprising: a) in response to a mobile terminal losing a firstconnection with a femtocell associated with a home mobile network andthen making a second connection with a macrocell associated with avisited mobile network, determining a network search parameter value fora mobile terminal, the value of the network search parameter beingdetermined in accordance with the number of network switches undergoneby the mobile terminal in a predetermined period of time; b)transmitting the network search parameter value to the mobile terminal;c) periodically re-determining the value of the network search parameterif the mobile terminal is still connected with the macrocell associatedwith the visited mobile network; and; and d) transmitting the networksearch parameter value determined in c) to the mobile terminal.

The first connection with the femtocell associated with the home mobilenetwork may be lost because the mobile terminal moves out of the areacovered by the femtocell, or because the apparatus which provides thefemtocell ceases to operate. Such an approach allows the mobile terminalto search for the home network in order to be able to switch back fromthe visited network to the home network as soon as is feasible.

The value of the network search parameter determined in a) may increasein accordance with the number of network switches undergone by themobile terminal in the predetermined period of time. The value of thenetwork search parameter may increase as the time for which the mobileterminal is connected to the mobile communications network increases.

According to a second aspect of the present disclosure there is provideda tangible data carrier for use in a computing device, the data carriercomprising computer executable code which, in use, performs a method asdescribed above.

According to a third aspect of the present disclosure there is providedan apparatus for use in a mobile communications network, the apparatus,in use, being configured to: i) determine a network search parametervalue for a mobile terminal, in response to the mobile terminal losing afirst connection with a femtocell associated with a home mobile networkand making a second connection with a macrocell associated with avisited mobile network, the value of the network search parameter beingdetermined in accordance with the number of network switches undergoneby the mobile terminal in a predetermined period of time; ii) transmitthe network search parameter value to the mobile terminal iii)periodically re-determine the value of the network search parameter ifthe mobile terminal is still connected with the macrocell associatedwith the visited mobile the network; and iv) transmit the network searchparameter value determined in iii) to the mobile terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 shows a schematic depiction of a mobile communications networkaccording to the present disclosure which comprises a first plurality offemtocells and a second plurality of macrocells.

FIG. 2 shows a schematic depiction of a further embodiment of acommunications network according to the present disclosure.

FIG. 3 shows a schematic depiction of a user equipment (UE) and theMobility Management Entity (MME) when an embodiment of the presentdisclosure is used in the context of LTE.

DETAILED DESCRIPTION

Mobile networks, for example as described above with reference to FIG.1, are often referred to as Public Land Mobile Networks (PLMNs). Amobile terminal will have a Home PLMN (HPLMN) which the terminal willconnect to in preference to all other PLMNs. When the mobile terminal isoutside of the coverage of the HPLM then it will connect to anothernetwork, known as a visited PLMN (VPLMN), in a process referred to asroaming. The VPLMN may be selected randomly from the PLMNs which areavailable to the mobile terminal, or there may be one or more higherpriority PLMNs which will be selected by the mobile terminal inpreference to other PLMNs.

When a mobile terminal is connected to a VPLMN it will occasionallysearch for its home PLMN, or one of the HPLMN's preferred PLMNs (PPLMN).This search is known as a higher priority PLMN search. Each mobileterminal will have a fixed parameter, T, which is normally programmedinto its SIM card. The parameter T is a multiple of 6 minutes and thedefault value, which is typically used in practice, is 60 minutes. Themobile terminal will perform the search for its home PLMN at thefrequency determined by the value of T. The default value of 60 minutesis typically used as it can minimize ping-pong effects, that is aterminal making repeated transfers between a first and a second network,and also prevents excessive battery consumption caused by searching fora higher priority PLMN.

The network that a mobile terminal is connected to can over-ride thevalue of the parameter T if it is determined that searches are beingmade too frequently. In such a case, the network can issue aMinimumPeriodicSearchTimer value to the mobile terminal. If theMinimumPeriodicSearchTimer value is greater than the value of the Tparameter then the MinimumPeriodicSearchTimer value will be used todetermine the frequency of searches for the home PLMN.

In the following discussion, a number of examples will be provided toshow how the MinimumPeriodicSearchTimer can be adjusted. As embodimentsallow the network operator to determine the frequency of PLMN searches,the T parameter in the mobile terminal SIM should be set to its minimumvalue. The current standards have a minimum value of 6 minutes but itwill be understood that this minimum value could be reduced further. Inthe absence of such limitations it will be understood that the Tparameter value could be ignored and the frequency of PLMN searches bedetermined entirely based on the MinimumPeriodicSearchTimer parametercommunicated from the network operator to a mobile terminal.

Table 1 below shows how the value of the MinimumPeriodicSearchTimerparameter can be varied with time. As can be seen from Table 1, searchescan be made on a more frequent basis shortly after a mobile terminal hasconnected to a VPLMN. As the time that the mobile terminal has beenconnected to the VPLMN increases then the time between successive PLMNsearches will increase. This is based on the fact that the failure ofthe more frequent PLMN searches to find the HPLMN (or a PPLMN) isindicative that the mobile terminal is not near to the HPLMN so the PLMNsearch frequency may be reduced. It will be understood that the time andMinimumPeriodicSearchTimer parameter values shown below in Table 1 aremerely exemplary and that other values may be used as long as theMinimumPeriodicSearchTimer parameter values increase with time.

TABLE 1 Variation of MinimumPeriodicSearchTimer parameter with time.Time (minutes) from Issue new MinimumPeri- entering VPLMNodicSearchTimer value of 0 2 12 6 36 12 120 60

Compared to a conventional mobile communications network using a fixedvalue for the PLMN search frequency, this embodiment of the presentdisclosure offers significant benefits. Overall battery usage is reduced(if the final value is larger than the fixed period that would haveotherwise been used) when not in coverage of a preferred PLMN, yet thelikely time to discover a preferred PLMN is quicker on average. In thisembodiment the network operator will determine appropriate parametervalues in order to balance the compromise between fast searches versusthe unwanted ping-pong effect and the reduction in battery life, basedon testing.

Other methods of determining the MinimumPeriodicSearchTimer parametervalue will now be described. The increasing ofMinimumPeriodicSearchTimer with time can be implemented without anyreference to the state or condition of the mobile terminals. Thefollowing methods rely, to some extent, on monitoring one or moreparameters from one or more mobile terminals. It will be understood thatthe method by which these parameters are reported by the mobileterminals is not of relevance to the present invention. Further data andor parameters which may be used to determine the value ofMinimumPeriodicSearchTimer may be generated or collected within thenetwork.

TABLE 2 Variation of MinimumPeriodicSearchTimer value with time andnumber of previous switches Issue new MinimumPeriodicSearchTimer valueof Time If 2 or If 1 If no (minutes) more PLMN PLMN PLMN from enteringswitch in X switch in X switch in X VPLMN minutes minutes minutes 0 12 62 12 12 12 6 36 12 12 12 120 60 60 60

Table 2 shows an example of how the value of MinimumPeriodicSearchTimermay vary in accordance with the time for which a mobile terminal hasbeen connected to a VPLMN and also the number of PLMN switches that havebeen made in a predetermined time period. The predetermined time periodmay have a value between 1 and 30 minutes, although larger values may beused.

It can be seen that mobile terminals which have made a greater number ofrecent network switches will search less frequently than mobileterminals which have made fewer (or no) recent network switches. Bydetermining the MinimumPeriodicSearchTimer in the manner described withreference to Table 2, the unwanted effects of too many frequent networkswitches (e.g. excessive battery usage and potential drop on quality ofexperience (QoE)) can be reduced whilst still giving users a greateropportunity to switch from a VPLMN to the HPLMN where it is available.

Mobility history for a mobile terminal in idle mode is not standardizedso the data on the timing and number of previous switches could comefrom a network management system, in either the home or visited network,or from the mobile terminal itself

TABLE 3 Variation of MinimumPeriodicSearchTimer value with location ofmobile terminal Issue new MinimumPeriodicSearchTimer value of Where noWhere Within expected HPLMN/PPLMN HPLMN/PPLMN coverage of expected edgeexpected HPLMN/PPLMN 255 30 2

Table 3 shows an exemplary set of MinimumPeriodicSearchTimer valueswhich vary in accordance with the location of the mobile terminal. Sucha method is of use as the location of the microcells and macrocells areknown and is unlikely to vary. If a mobile terminal is within expectedcoverage of the HPLMN (or a PPLMN) then it will be preferred that themobile terminal switch from a VPLMN to the HPLMN quickly. Similarly, ifit can be determined that the mobile terminal is outside the coverage ofthe HPLMN then HPLMN searches should be carried out infrequently toreduce battery drainage. It will be understood that the location of themobile network may be determined by the network, for example using wellknown triangulation methods, or by the mobile terminal reporting its ownlocation, for example based on GPS circuitry within the terminal. Mobileterminals are likely, by definition, to vary their location and thus theterminal location should be determined on a periodic basis, for exampleevery 30 minutes, and the MinimumPeriodicSearchTimer determinedaccordingly.

Table 4 shows an exemplary set of MinimumPeriodicSearchTimer values fora further method in which the values are determined in accordance withboth the location of the mobile terminal and the time since it connectedto the VPLMN. Such a hybrid approach prevents the unwanted effects ofregular PLMN searching (i.e. excessive battery usage) in the event thatit is not possible to switch to the HPLMN despite the location of themobile terminal indicating that such a switch is feasible.

TABLE 4 Variation of MinimumPeriodicSearchTimer value with time andlocation of mobile terminal Time Issue new MinimumPeriodicSearchTimervalue of (minutes) Where no Where Within expected from enteringHPLMN/PPLMN HPLMN/PPLMN coverage of VPLMN expected edge expectedHPLMN/PPLMN 0 60 6 2 12 60 12 6 36 60 12 12 120 255 60 60

Table 5 shows a further example of how MinimumPeriodicSearchTimer valuescan be determined, in this case in accordance with a condition of themobile terminal, for example the remaining battery charge. The batterycondition may be reported periodically by the mobile terminal, or thenetwork may poll the terminal periodically to obtain the data. Thus, thesearch frequency may be adjusted in order to maintain battery life bymaking searches less frequent as battery life decreases.

TABLE 5 Variation of MinimumPeriodicSearchTimer value with batterycondition Battery lifetime at Issue new MinimumPeri- most recent updateodicSearchTimer value of >50% 2 50% > 25% 6 25% > 15% 60   15%> 255

The way battery life is reported is likely to be vendor specific.Battery life may then be reported by methods such as a percentage ofexpected battery life remaining, as descriptors such as low/medium/high,or as a number of mW hours remaining. The operator may also useknowledge of the power consumption behaviors of various handsets and/orusers when deciding on the appropriate action.

The method described above with respect to Table 5 may also be used inconjunction with the other methods described above so that theMinimumPeriodicSearchTimer value indicated by the battery level may actas a threshold so that other methods may be used to determine theMinimumPeriodicSearchTimer but that value would be only be used if itindicated a MinimumPeriodicSearchTimer value greater than that indicatedby Table 5 (that is, searches would only be performed at a lowerfrequency than that indicated by Table 5).

Table 6 shows a yet further set of MinimumPeriodicSearchTimer values,which are determined in accordance with one or more user preferences.

TABLE 6 Variation of MinimumPeriodicSearchTimer with user preferenceIssue new MinimumPeriodicSearchTimer value of Where user Where user UserUser wants to wants to concerned concerned Battery maximize minimizeabout about lifetime at battery roaming battery roaming most recent lifeat charges at more than more than update all costs all costs roamingbattery >50% 255 2 6 2 50% > 25% 255 2 12 6 25% > 15% 255 2 60 12   15%>255 2 255 60

Table 6 shows an example where the user is given the option fromselecting from 4 profiles which indicate their preferences, for examplein prioritizing battery life over the cost of roaming (which may beincurred by using a VPLMN and is likely to be passed on to the user by anetwork operator) and vice versa. The MinimumPeriodicSearchTimer valuesare then determined in accordance with the selected profiles, as can beseen from Table 6.

It will be understood that other schemes for determiningMinimumPeriodicSearchTimer values in accordance with user preferencesmay be devised. For example, a user may be able to send real time QoEdata to the network (for example, the user's mobile terminal may run aQoE reporting application), and possibly also the reasons for a givenQoE, for example the fact that the battery is running low, or that thebattery is draining quickly. The data from such reports may then be usedto determine a MinimumPeriodicSearchTimer value.

A simple example could be to set:

-   -   Minimum possible value for MinimumPeriodicSearchTimer=2 mins    -   Maximum possible value for MinimumPeriodicSearchTimer=240 mins    -   Start MinimumPeriodicSearchTimer value=6 minutes    -   when User reports decrease in QoE due to battery issues, double        the MinimumPeriodicSearchTimer value    -   when User reports QoE drop due to high amount of roaming        charges, halve the MinimumPeriodicSearchTimer value        with the MinimumPeriodicSearchTimer value being kept within the        bounds set by the maximum and minimum values.

It will be understood that such a preference-based approach could alsoincorporate some of the mechanisms described above, i.e. setting athreshold value based on battery level, varying theMinimumPeriodicSearchTimer value in accordance with the terminallocation or time connected to the VPLMN, etc.

Table 7 shows a still further example of how theMinimumPeriodicSearchTimer value can be varied in the event of a failureof the HPLMN. If one or more of the microcells which are part of theHPLMN were to fail for a short period of time then this failure can besignaled to the operator of the VPLMN (or VPLMNs) to which the mobileterminals will connect (the operators of the VPLMN(s) may be able toinfer the failure of the HPLMN based on the sudden number of roamingconnections being made in one or more concentrated locations).

TABLE 7 Variation of MinimumPeriodicSearchTimer with networkavailability Probability that HPLMN Issue new MinimumPeri- now availablein area odicSearchTimer value of >95% 2 95% > 50% 6 50% > 5%  20    5%>255

If the mobile terminal were to determine the MinimumPeriodicSearchTimervalue in accordance with some of the methods discussed above then theremay be many frequent searches made even though there may be no HPLMN toswitch to. Thus, if the MinimumPeriodicSearchTimer values are determinedas set out in Table 7 then when there is a very low likelihood of theHPLMN being available (i.e. very shortly after failure) then there is avery high MinimumPeriodicSearchTimer value, which will reduce as thelikelihood of the HPLMN being available increases. The likelihood of theHPLMN being available may be inferred based on the time since thefailure. When the service is restored then this information can be sentto the VPLMN so that a very low MinimumPeriodicSearchTimer value istransmitted to the mobile terminals so that the mobile terminals canswiftly re-connect to the HPLMN.

Table 8 shows a variant of the method discussed above with respect toTable 7, in which the determination of the MinimumPeriodicSearchTimervalue is also made with respect to the number of mobile devices whichare be looking to switch back to the HPLMN. Such control of the searchfrequency can prevent too much signaling from occurring in a short spaceof time.

TABLE 8 Variation of MinimumPeriodicSearchTimer with networkavailability and number of terminals requiring to switch to the HPLMN.Issue new MinimumPeriodicSearchTimer value of Number of Number ofProbability Number of devices devices Number of that HPLMN deviceslooking for looking for devices now available looking for HPLMN HPLMNlooking for in area HPLMN >50 50 < 20 20 < 10 HPLMN <10 >95% 60 6 6 295% > 50% 60 20 12 6 50% > 5%  120 60 60 20    5%> 255 255 255 60

In the examples described above, the network would have to go intoconnected mode in order to be able to receive parameter values, or othersimilar data from one or more mobile terminals. This connection may beinitiated either by network or by the mobile terminal. Data could betransferred to the network either during the next scheduled connectionor a connection may be initiated for the purpose of transferringparameters. The signaling overhead required to make such a connectionmay be a factor which is taken into account when determining thefrequency of updates. It will be understood that parameters could alsobe generated from within the network, either a VPLMN or a HPLMN. Theseparameters may then be reported to a base station which is incommunication with the mobile terminal.

The determination of a MinimumPeriodicSearchTimer value may be made in adistributed manner, that is the values are calculated for each mobileterminal by the respective base station. Alternatively, centralizedcalculations may be made, with the parameter values being issued to allthe respective mobile terminals, for example from the MobilityManagement Entity (MME). The parameters may be transmitted to the mobileterminals using a non-access stratum (NAS) message, which allows theparameter to be sent to one or more terminals as required.

In some of the methods discussed above, the determination of a value ofMinimumPeriodicSearchTimer is based on monitoring one or moreparameters. These parameters would typically come from the mobileterminal. It will be understood that the specific manner in which theseparameters are reported is not relevant to the operation of embodimentsof the present disclosure. For example an application could run on thephone, which sends periodic or threshold based updates, to anapplication server. The application server would then send the relevantinformation to the base station (or eNodeB in the context of LTEnetworks). An alternative could be to upgrade the specification oflogged minimisation of drive testing (MDT) reporting. After each updatea network may decide to take action to updateMinimumPeriodicSearchTimer.

The granularity of HPLMN searching in 3GPP can only go down to multiplesof 6 minutes at the moment. Embodiments of the present disclosure makeit possible to determine MinimumPeriodicSearchTimer values with smallergranularities which could be fed into 3GPP standardization. It will beunderstood that embodiments of the present disclosure could be usedwithin the context of the present standards with a value ofMinimumPeriodicSearchTimer being determined in a manner as described andthen being rounded to the nearest multiple of 6 minutes.

FIG. 2 shows a schematic depiction of a further embodiment of acommunications network 100′ according to an embodiment of the presentdisclosure. Network 100′ comprises a plurality of femtocells 110 a, 110b, 110 c and a single macrocell 120. All of the plurality of femtocellsare contained within the area covered by the macrocell 120. Themacrocell is provided using a conventional cellular base station 122,which has a backhaul network connection 125 to a switch 127 which allowsdata and/or voice signals to be routed to and from the base station, andthence to cellular terminals which are connected to the cellular basestation. The switch 127 is further connected to a core communicationsnetwork 128. The macrocell provides an LTE interface but may alsoprovide further radio interfaces such as GSM, 3G etc.

Each of the femtocells 110 a, 110 b, 110 c are provided by a respectivewireless access point 112 a, 112 b, 112 c. The wireless access pointseach have a respective connection to an exchange building 116, whichhouses a switch 117 which allows data to be sent to and from thewireless access points. The switch 117 is further connected to a corecommunications network 118. Wireless access point 112 a is connected tothe exchange using a copper cable 113 with the data being transportedusing, for example, ADSL technology which can provide up to 24 Mbit/s.Wireless access points 112 b & 112 c both have copper cable connections113 to a cabinet 114 which houses VDSL equipment. The cabinet 114 isthen connected to the exchange using an optical fibre connection 115.VDSL technology can be used to transport data at rates of up to 80Mbit/s.

The wireless access points may preferably comprise a conventionalinternet router and WiFi access point which further comprises anappropriate radio interface, such as LTE, to allow it to function as awireless access point for a cellular network. It will be understood thatother network technologies may be used to connect the wireless accesspoints to the exchange (for example, fiber to the premises (FTTP), pointto point radio, etc) and that this is not relevant to the operation ofembodiments of the present disclosure.

When a mobile terminal is turned on within the coverage of one of thefemtocells 110 then it will connect to the femtocell as the plurality offemtocells form a part of the HPLMN. When the HPLMN is lost to themobile terminal (see below) then the mobile terminal will connect to themacrocell 120, which forms part of a VPLMN. As discussed previously, itis preferred that as much traffic be carried over the HPLMN as possible,in order to maintain network capacity on the VPLMN and to reduce anycost which may be incurred by sending traffic over the VPLMN. Thus, themobile terminal will seek to transfer back to the HPLMN as soon asfeasible, with the PLMN search frequency being selected and/or varied inaccordance with one of the methods described above.

It will be understood that even if there are a large number offemtocells within the area covered by a single macrocell then there willbe significant areas of the macrocell which are not covered by afemtocell. Thus, if a mobile terminal is moving then it is likely thatit will move out of femtocell coverage and will need to handover to themacrocell.

Furthermore, it is likely that the availability of a given femtocellwill be less than that of the macrocell base station. The wirelessaccess points are likely to be provided in domestic and commercialproperties in the same manner that WiFi hotspots are currently provided.Thus, they may be disconnected or powered off if the property is notoccupied; if the ADSL/VDSL connection were to fail then the wirelessaccess point would not be able to operate properly; the loss ofelectrical power to the property would cause the wireless access pointto fail (whereas base stations are normally provided with battery backuppower systems); the wireless access point may be power cycled in attemptto clear a fault, etc. Regardless of the cause of the failure of thewireless access point, the mobile terminal will need to handover to themacrocell and then seek to move back to a femtocell as soon as isfeasible.

Such a mobile terminal may comprise a smart phone, tablet, or othermobile computing device (see below). An app may be provided to controlthe operation of the mobile terminal such that an appropriate PLMNsearch frequency can be selected and then varied as needed. This app maycontain data regarding the likely location of femtocells, for examplebased on the address of customers who have suitably equipped wirelessaccess points in their premises. The mobile terminal can determine itslocation, using known techniques, and then calculate the likelihood thata wireless access point is in range. Depending on the result of thiscalculation then the PLMN search frequency may be varied accordingly.

As the wireless access point is likely to also provide WiFiconnectivity, if the app detects that the mobile terminal hasre-established a WiFi connection subsequent to the connection being lostthen this can be used to infer that there is a high probability that theterminal is within the coverage of a femtocell. This inference can bestrengthened by identifying the provider of the WiFi service that themobile terminal is connected to. This can be achieved by checking theSSID of the WiFi access point (for example ‘BT WiFi’) or by matching theIP address assigned to the WiFi interface with a predetermined range ofIP addresses used by the network operator. This inference can be used tochange the PLMN search frequency or can be a prompt which initiates ahandover from the VPLMN to the HPLMN.

FIG. 3 shows a schematic depiction of a user equipment (UE) 200 and theMobility Management Entity (MME) 300 when an embodiment of the presentdisclosure is used in the context of LTE. As will be understood by thosewho are skilled in the relevant technical field, the communicationsbetween the UE and the MME will be routed via the eNodeB which isomitted from FIG. 3 for the sake of clarity.

The UE 200 comprises a SIM 210, PLMN search function 220 and userpreferences 230. The MME 300 controls a number of different UE controlfunctions and uses the NAS (non-access stratum) 400. The NAS is afunctional layer in the LTE protocol stacks which is used to carrydialogue between the UE and the network nodes. The NAS will store aplurality of management object parameters 410 for transmission to theUEs. The various functions and entities required to implement thepresent invention 500 comprise a UE timer 510, look-up table 520, aMinimumPeriodicSearchTimer algorithm 530, operator preferences 540, UEcapabilities 550, user preferences 560 and a MinimumPeriodicSearchTimerupdate function 570.

The UE SIM 210 stores a value for T, which can determine the frequencyof PLMN searches if it is less than the MinimumPeriodicSearchTimerparameter value. It will be understood that this is a feature of thepresent standards and that these standards could be modified so that theMinimumPeriodicSearchTimer parameter value provided by the networkoperator takes priority over the T parameter value stored in the SIM.The SIM also stores data regarding the HPLMN and one or more PPLMNs. ThePLMN search function carries out the search for a PLMN and is activatedin accordance with the MinimumPeriodicSearchTimer parameter valuedetermined as described above. User preferences 230 store a number ofdata parameters and measurements which can be reported to the networkperiodically, as described above. These parameters may include, forexample, battery condition, UE location, QoE, QoE preferences, etc. andhistorical values and trends for one or more of these parameters andvalues.

As described above, the MinimumPeriodicSearchTimer algorithm 530 willdetermine a value for the MinimumPeriodicSearchTimer parameter based onthe inputs received from one or more of the UE timer 510, operatorpreferences 540, UE capabilities 550, and the user preferences 560. Thealgorithm may be prompted to retrieve a MinimumPeriodicSearchTimer valuefrom the look-up table 520 dependent on the outcome of thedetermination. It will be understood that the UE timer, UE capabilitiesand the user preferences will need to be stored and/or determined on aper user basis. The operator preferences may be stored and/or determinedon a per user basis or for a group of one or more UEs. When a newMinimumPeriodicSearchTimer parameter value is determined for aparticular UE then the value will be sent to theMinimumPeriodicSearchTimer update function 570, which will cause the newparameter value to be sent to the UE, as a management object parameter.

It will be understood that the various functions and entities requiredto perform embodiments of the present disclosure 500 can be implementedwithin a MME using appropriate software. Similarly, a conventionalmobile terminal (which may be a mobile telephone, smartphone, or othermobile device) may be upgraded to be able to perform embodiments of thepresent disclosure by the installation of one or more apps or othersoftware. Suitable computer code may be deployed to such devices viadownload, for example via the internet, or on some physical media, forexample, DVD, CD-ROM, USB memory stick, etc. for which the device has anappropriate media reader.

In summary, the present disclosure provides a method for moreefficiently managing a mobile communications network by varying thefrequency with which a mobile terminal searches for a home network.

A detailed listing of all claims that are, or were, in the presentapplication, irrespective of whether the claim(s) remain(s) underexamination in the application is presented below. The claims arepresented in ascending order and each includes one status identifier.Those claims not cancelled or withdrawn but amended by the currentamendment utilize the following notations for amendment: 1. deletedmatter is shown by strikethrough for six or more characters and doublebrackets for five or fewer characters; and 2. added matter is shown byunderlining.

1. A method of operating a mobile communications network, the methodcomprising: a) in response to a mobile terminal losing a firstconnection with a femtocell associated with a home mobile network andthen making a second connection with a macrocell associated with avisited mobile network, determining a network search parameter value fora mobile terminal, the network search parameter value being determinedin accordance with the number of network switches undergone by themobile terminal in a predetermined period of time; b) transmitting thenetwork search parameter value to the mobile terminal; c) periodicallyre-determining the network search parameter value if the mobile terminalis still connected with the macrocell associated with the visited mobilenetwork; and; and d) transmitting the network search parameter valuedetermined in c) to the mobile terminal.
 2. A method according to claim1, wherein of the network search parameter value determined in a)increases in accordance with the number of network switches undergone bythe mobile terminal in the predetermined period of time.
 3. A methodaccording to claim 1, wherein the network search parameter valueincreases as the time for which the mobile terminal is connected to themobile communications network increases.
 4. A method according to claim1, wherein the network search parameter value is an integral multiple of6 minutes.
 5. A tangible data carrier for use in a computing device, thedata carrier comprising computer executable code which, in use, performsa method according to claim
 1. 6. An apparatus for use in a mobilecommunications network, the apparatus, in use, being configured to: i)determine a network search parameter value for a mobile terminal, inresponse to the mobile terminal losing a first connection with afemtocell associated with a home mobile network and making a secondconnection with a macrocell associated with a visited mobile network,the network search parameter value being determined in accordance withthe number of network switches undergone by the mobile terminal in apredetermined period of time; ii) transmit the network search parametervalue to the mobile terminal; iii) periodically re-determine the networksearch parameter value if the mobile terminal is still connected withthe macrocell associated with the visited mobile the network; and iv)transmit the network search parameter value determined in iii) to themobile terminal.
 7. An apparatus according to claim 6, wherein thenetwork search parameter value determined in i) increases in accordancewith the number of network switches undergone by the mobile terminal inthe predetermined period of time.
 8. An apparatus according to claim 6,wherein the network search parameter value increases as the time forwhich the mobile terminal is connected to the mobile communicationsnetwork increases.